A plasma processing apparatus is described in Patent Document 1. The plasma processing apparatus disclosed in Patent Document 1 includes a processing chamber, a stage, a microwave generator, an antenna, a dielectric window, a coaxial waveguide, and an injector base.
The stage is accommodated in the processing chamber, and a processing target substrate is mounted on the stage. The antenna is provided above the stage. The antenna is connected with the microwave generator via the coaxial waveguide. The antenna includes a slot plate having slots. The dielectric window is provided between the antenna and a processing space above the stage.
The dielectric window has a space for accommodating therein the injector base and also has a through hole extending from that space toward the processing space. The injector base is prepared by forming an Y2O3 film on an aluminum base. The injector base has a through hole.
In this plasma processing apparatus, a processing gas is introduced into the processing space through a hole inside an inner conductor of the coaxial waveguide, the through hole of the injector base, and the through hole of the dielectric window.    Patent Document 1: Japanese Patent Laid-open Publication No. 2010-021243
The present inventors have conducted researches for further suppressing particle generation in the plasma processing apparatus as disclosed in Patent Document 1 and have found out that a small number of particles having a diameter of several tens of nanometers may be generated when a fluorine-based processing gas is used.